I have heard that there are ways to convert the A/C compressor on Jeeps to serve as an on-board air compressor. Since space is at a premium, especially under the hood, is this true and if so, where and how is this done? I have A/C in my 92 Cherokee limited but it blows warm so why not convert it if possible?   

the short of it is; put a filter on the low side, and a air fitting on the high side, then charge the clutch when you want  air.

the problem is getting oil to the compresser. normaly theres lubricant in the freon. people do it, but its becaus of that problem the most use yorks for onboard air

Some of the guys that I have talked to use a few drops of sewing machine oil in the compressor every once and a while to keep it lubed and put a filter for a small aircompressor on the outlet side to keep oil out of the tank and or air lines.